(i) Field of the Invention
This invention relates to a process for isolating cholesterol from eggs. In particular, this invention relates to a process for isolating cholesterol from dried whole egg or from dried egg yolk obtained from domestic hen eggs, thus providing not only free cholesterol, but also providing edible whole egg that is reduced in cholesterol or edible egg yolk powder that is reduced in cholesterol.
(II) Description of the Prior Art
Cholesterol is a suitable precursor in recently developed routes to chemical substances used for oral birth control, as well as in routes to substances that can be used for production of Vitamin D, and in the manufacture of derivatives which are used in liquid crystal devices. Consequently, many procedures have been developed for isolating cholesterol from materials containing cholesterol. Most of these methods heretofore used merely relied on the use of a solvent to extract the cholesterol from the raw material under specified conditions. For example, U.S. Pat. No. 2,371,467 to Porsche describes a process for isolating cholesterol from animal nerve tissue by extracting cholesterol from the tissue with ethylene dichloride. Thus, many of the above-described procedures produced crude, rather than substantially pure, cholesterol. Canadian Pat. No. 498,384 issued Dec. 15, 1953 to Armour & Co. purported to be an improvement on those procedures by providing a process for treating crude cholesterol by dissolving the cholesterol in an alkali metal hydroxide solution containing 85% alcohol, then crystallizing cholesterol from solution, and finally washing the crystallized cholesterol.
However, this procedure suffers the deficiency that it is generally not utilizable to provide cholesterol directly from the raw cholesterol-containing material, and the by-products from which the cholesterol has been removed are generally not useful.
Eggs from domestic hens (hereafter referred to as eggs) are constituted of water, protein, fat (including cholesterol), carbohydrate, minerals, and vitamins. The average representative compositions of these materials in eggs is tabulated below in Table I.
TABLE I ______________________________________ Approximate Composition (g per 100 g of Constituent whole raw egg) ______________________________________ water 74 protein 13 fat 11 (cholesterol) (0.76) carbohydrate 0.7 minerals 1 vitamins ______________________________________
It has long been recognized that eggs are a most desirable food in contributing to the nutritional requirements of man. Unfortunately, as pointed out above, the yolk of egg is one of the richest sources of dietary cholesterol. Cholesterol from egg yolk-containing foods contributes increased serum cholesterol levels that are often associated with heart and circulatory diseases. In addition egg fat possesses a low ratio of polyunsaturated to saturated fatty acids. In the past years emphasis has been placed on the desirability of reducing dietary intake of cholesterol and of reducing the amount of the more saturated fats and replacing them with polyunsaturated fats. The resulting dried egg product from which the free cholesterol has been virtually eliminated is considered desirable in the nutrition of persons with cardiovascular disease problems. Consequently, Canadian Pat. Nos. 898,056 issued Apr. 18, 1972 to Corn Products Company and 903,552 issued June 27, 1972 to CPC International Inc. provide procedures for removing cholesterol by extracting dried egg yolk solids with a non-polar solvent, e.g., n-hexane, to remove the readily extractable cholesterol.
A major deficiency of this procedure is that the defatted egg yolk material may contain 150 ppm or more of a residual solvent. Such n-hexane solvent is not a desirable constituent of a food product and hence the defatted egg yolk material is not optimally edible.